Presentation on the Fundamental of Mechanical Seal

1. PEM 3 KNOWLEDGE SHARING PRESENTATION
FUNDAMENTALS OF MECHANICAL SEAL
Presented by
Emmanuel Raphael Essen
(MNIMechE, MNIM, ISMN)
October, 2014
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2. Tables of content.
 Historical development of a Mechanical seal
 What is Mechanical Seal
 Reason for using Mechanical seal
 Advantages of Using cartridge seal.
 Types of seals:
 Essential elements of a mechanical seal
 Mechanical seal Components
 Essential requirements for proper operation of a mechanical seal
 The fluid in the pump and seal area, Leakage, Seal failures and Leakage Rate.
 Effective forces in a mechanical sealPower consumption of a liquid lubricated
mechanical seal
 Seal Face Material
 Power Consumption
 Classification of Mechanical Seal
 Many factors need to be considered in the application of a mechanical seal
 Mechanical seal application limit
 Seal faces loading devices
 Flush arrangement
 Selecting a Mechanical seal
 Mechanical seal piping plan
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3. Historical Development of a Mechanical seal
At the beginning of the nineteenth century, many endeavours were made to
develop a replacement for the conventional, braided packing used for piston
pumps and rotating shafts.
A more reliable system for different kinds of liquid-conveying rotating machinery
was desired.
By the 1930’s, the James Walker Group came up with a mechanical shaft seal for
refrigeration compressors. At the same time, the John Crane company invented the
first automotive mechanical shaft seal. In the early 1940’s, the company developed
and introduced the patented elastomer bellows axial shaft seal, today known as
“Type 1”.
After this breakthrough in sealing technology, other types of mechanical shaft
seals were developed. With several types of mechanical shaft seals, the John Crane
company adopted the tagline, “The right seal for the right application”.
Today, John Crane is still a leading seal manufacturer along
with Grundfos, Burgmann, Flowserve, etc.
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4. What is Mechanical Seal
Mechanical seal is a sealing device for any rotating equipment which prevents
the inner fluid from leaking through the clearance between the rotating shaft and
the housing case. There are various types of mechanical seals for each
application and operating condition of the equipment but in principle,
mechanical seal is a face type seal, which performs sealing by two sealing faces
vertical to the shaft.
Mechanical Seal incorporates various components such as the spring giving
contact force and the packing which eliminates intrusion of the fluid from the
outside. The seal face is an accurately flat face, and so if it is worn, it does not
cause the leakage of the sealant as far as wear is within the maximum allowable
amount.
Therefore it can be used for a long time free of maintenance, and is very
effective and efficient in terms of reliability and economy
Mechanical seals are used not only in pumps but also in other various equipment
such as mixers, agitators, compressors, rotary unions, submersible motors, etc.
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5. Reasons for using Mechanical seal:
 To minimize leakage
 To prevent toxic fluids escaping to atmosphere
 To reduce power loss.
Advantages of Using cartridge seal.
By using cartridge seals the following can be achieved:
 Reduced skill base
 Increased Reliability
 Fits multiple types of pumps
 Reduced downtime
 Increased operating profits.
Types of seals: Static Seals & Dynamic Seals
STATIC SEALS: Sealing takes place between two parts that don’t move in relation
to each other.
Application - Pipe flanges ,vessel /Tower nozzles, pump casing joint. - Fan /Blower
casing joint , Compressor casing joint. - Turbine casing joint, Heat exchanger joints
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6. Types: Gaskets , O-rings etc
GASKET: Packing designed to go between two rigid parts in stationary conditions
May be in form of sheet , strip , bulk. Properties: Impermeability, Ability to flow
into joints, Corrosion resistance
DYNAMIC SEALS: Used for sealing fluid between parts that move in relation with
each other.
Application: Centrifugal pump gland, valve gland , bearing housing
Turbine/compressor inter stage and end sealing , Reciprocating compressors cylinder
sealing
TYPES: Gland packings, Mechanical contact seals, Labyrinth seal, Oil seal, Oil film
seals
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7. Essential elements of a mechanical seal
The basic design of the Mechanical seal consists of the following elements:
Flexibly mounted seal face, Rigidly mounted seal face, Compression
device and Secondary seal
Mechanical seal Components
 Rotary seal face
 Stationary seal face
 Springs
 Retainer
 Sealing /flushing media
 O-rings
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8. Essential Requirements for Proper Operation of a Mechanical Seal
These are the essential requirements:
 Seal faces must be flat and polished.
 Seal faces must be installed perpendicular to the shaft.
 Spring force must be sufficient to maintain contact of the faces
The Fluid in the Pump and Seal Area
Key Point: The fluid contacts the seal faces and other parts in wide open areas, in
very small gaps and at the exit of the seal faces. Pressure and temperature of the
fluid will depend on its location and determine its respective state, i.e. liquid,
gaseous, solid or a mixture.
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9. Leakage:
A few facts about the leakage (and wear) behavior of contacting mechanical seals:
It is essential for proper lubrication and wear of the faces.
Normal leak rates range between immeasurably small to steady drips or temporary to
even small steams. Some seals leak some of the time, some seals never leak
(measurably), and some leak all the time.
Leakage patterns can be constant, progressive or erratic in nature.
It can be in liquid, gaseous and/or solid state.
Successful contacting seals tend to have very low wear rates and low leakage rates.
Some forms of contact is necessary for low leakage rates. Non-contacting or “full lift
off” seals (hydrostatic or hydrodynamic tend to have visible, sizeably larger leakage
rates.
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10. The large majority of mechanical seals never wear out and are removed from
service for some other reason.
Seal failures
Seal failure occur for a wide range of reasons. Type of seal failures
 Lubrication failures: Dry running and poor lubrication
 Contamination failures: Clogging, Hang-up, Particles deposits, Sticking
and seizure.
 Chemical, physical degrading and wear: Ageing and swollen rubber
parts, Corrosion, wear, Explosive decompression
 Installation failures: Shaft misalignment, seats not mounted
perpendicular to the shaft, axially moving shaft and wrong assembly
length.
 System failures: The pressure in the seal chamber, the temperature around
the shaft seal in the seal chamber, the pumped medium, the speed, the shaft
seal dimensions.
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11. Leakage rate:
The leakage rate of a mechanical shaft seal depends of a number of
factors such as:
 Surface roughness of seal faces
 Flatness of seal faces
 Vibration and stability of pump
 Speed of rotation
 Temperature, Viscosity and Type of pumped medium
 Pump pressure
 Seal and pump assembly.
.
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12. Effective forces in a Mechanical Seal
These are the forces operating in mechanical seals:
 Axial and radial forces
 Closing and opening forces
 Hydrostatic and hydrodynamic forces
Seal Face Materials: Few materials are suitable for seal faces. To keep
leakage as low as possible, the seal gap must be very small. As a result, the
lubricating film is very thin.
Consequently, the seal face materials must be able to withstand rubbing
against each other at high load and speed.
The best seal face materials have low friction, high hardness, good corrosion
resistance and high heat conductivity.
Examples of seal face materials: Carbon graphite, Aluminium Oxide
(Alumina), Tungsten carbide, Silicon carbide, Diamond coatings
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13. Power Consumption of a liquid lubricated mechanical seal
Important Points:
Face friction, churning and soak in heat.
Flush to dissipate the heat in order to control the gap temperature.
Coefficient of friction can swing considerably during operational transients.
The key is to maintain the gap profile as parallel as possible, i.e.minimize distortions.
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14. Classification of Mechanical Seal
Mechanical seals are classified by arrangement and configuration.
The wide variety of seal types is due to the diversity of applications each
utilizing different machinery, fluids and processes.
Selection of the best type is not always easy and straight forward as there is
usually a compromise between economical and technical factors.
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15. CLASSIFICATION BY ARRANGEMENT:
1. SINGLE SEALS: (a) Single internally mounted seal, (b) Single
externally mounted seal
Inside mounted = pressure on outside diameter of parts
Outside mounted = pressure on inside diameter of parts
The inside mounted mechanical seal is most popular type of single
mechanical seal.
Most seals are designed to leak so that the liquid or gas will lubricate the seal
faces. Applications that do not utilize substances that must be contained,
such as hazardous gases, dangerous chemicals or flammable liquids, will
generally use single seals. E.g P-1560, P-1570
Inside Mounted-Pressure on
outside diameter of the parts
Outside Mounted-Pressure on inside
diameter of the parts
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16. 2. Dual seals
Pressure between seals is higher than seal chamber pressure (typically min. 30
psig).
External fluid lubricates both sets of faces.
Leakage to the atmosphere is external fluid.
Is also called a "Double seal".
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17. Pressure between seals is lower than seal chamber pressure (typically
atmospheric).
External fluid only lubricates the most outside set of faces. The most inside
faces are lubricated with the pumped fluid. The most outside seal serves as a
safety seal or containment device.
Leakage to the atmosphere is external fluid, possibly mixed with small amounts
of pumped fluid.
Is also called a "Tandem seal".
DOUBLE SEALS: (a) Back to back seals (b) Face to face seals © Tandem
seals
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18. Faces can be configured in several ways: face to back, face to face and back to back.
Mechanical seal classification by Consfiguration i.e.design
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19. 1. Design: Pusher vs. Non-pusher and Balanced vs. Non-balanced
Pusher vs. Non-pusher
Pusher seals utilize a dynamic secondary seal which moves axially with the major
seal face. Non-pusher seals have a static secondary seal which stays stationary
against the shaft or sleeve.
Defined by the secondary seal type: o-ring or polymer wedge versus bellow, rubber or metal.
Balanced Vs Non- balanced
Balanced Seal:
 Reduced closing forces
 Reduced power consumption
 For pressure up to 3000 psig
 Always recommended for volatile liquids
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20. Non- balanced:
 High closing forces
 Low leakage
 For pressure up to 200 psig
 Not recommended for volatile liquids
2. Face Pattern
Examples are hydro-grooves, wavy faces, tapered faces.
Intended to increase opening forces in order to improve lubrication.
Friction is reduced at the expense of a higher leak rate.
3. Stationary Spring Seals and Rotating Spring seals
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21. Stationary spring seals are recommended by high speeds > 5000 ft/min.
Stationary spring seals are more suitable for machinery with inherently larger
tolerances such a heavy duty slurry pumps and older pumps which have looser
tolerances.
4. Cartridge seals and split seals
Cartridge seals
 Seal are pre-assembled with sleeve and flange in one unit.
 Easy to install.
 No measurements during installation.
 Spring load is preset.
 May be factory tested with air, water or oil.
 More costly as compared to component seal.
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22. Split seals
 Seat is axially split.
 Does not require disassembly of the pump to install = reduce down time.
 Leaks more than a conventional seal.
 More costly as compared to conventional seal.
Classification by containment devices
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23. Factors need to be considered in the application of a mechanical seal
Here are some of the factors that need to be considered:
 Pressure & speed (PV limit = Pressure x Velocity).
 Temperature.
 Fluid properties or characteristics.
 Run out of the shaft.
 Seal chamber type, available space radial and axial.
 Flushing/cooling arrangements, utilities in the plant.
 Mode of operation of the pump in the plant: continuous, cyclic, multi-
 purpose.
 Static versus dynamic pressure.
 Test requirements.
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24. Mechanical Seal Application Limit
General application guide per seal type
Seal Type Applications
Non-pusher elastomeric bellows seal A - B - D - E - L
Non-pusher metal bellows seal A - D - E - F - I - J - L
Pusher O-ring secondary seal A - B - G - H - K
Pusher polymer seal A - B - G - K
Pusher stationary slurry seal A - B - C - D - E - F - M
Pusher split seal A - B - K
Pusher dual gas seal A - B - E - F - G - H - L
Fluid - Characteristics
A - Clean Lubricating
B - Clean Non-lubricating
C - Viscous
D - Clogging / Scaling / Polymerizing / Fibrous
E - Crystallizing
F - Molten Liquid
G - Corrosive - Acids
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25. H - High Vapor Pressure
I - Cryogenic
J - High Temperature (> 260 ºC / 500 ºF)
K - Solids (< 0.1% by volume and less than 10 micrometers (394 micro
inches) in size.
L - Solids (< 2% by volume and less than 10 micrometers (394 micro inches)
in size
M - Solids (> 2% by volume).
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26. Seal Faces Loading Devices
Description of seal faces loading devices
Wide variety of types but they can be categorized as either a
spring or a bellows of some kind.
Working of a seal face loading devices
Seal face loading devices impart an axial load to maintain contact
when there is no hydraulic pressure from the pumped medium.
At higher pressures the spring force is only a small fraction of the
overall face pressure.
At face speeds above 5000 ft/min the spring element is installed
stationary because of the centrifugal effects.
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27. Flush arrangements
It refers to the various methods used to lubricate, cool and remove
deposits and heat in mechanical seal.
Purpose of Flush:
 Introduce fluid into seal chamber to improve the lubrication.
 Work to support the piping plan.
 Removal of seal generated heat.
 Removal of vapor bubbles.
 Protect against erosion
Selecting a mechanical seal
The mechanical seal should be selected according to the operating
conditions at the seal location. These important factors must be
considered when selecting a mechanical seal:
 • Shaft seal diameter
 • Type of pumped medium
 • Temperature
 • Sealing pressure
 • Shaft speed of rotation.
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28. See next slides
for
Seal Piping plan
P-1560, P-1570, P-
1580, P-1101 and P-
4101
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For P- 1560, P-1570 and P-1580
Propane Reflux Pump (De-propanizer ), De-butanizer Reflux
pump and LPG Re-injection Pumps.
The sealant is supplied from a common sealant system (A-1502)
which supplies the P-1560, P-1570 and P-1580 pumps.
Mechanical seal system of a single unit has the following:
Accumulator
Heat Exchanger
Pressure guage
Temperature guage.
See Plan 53c

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P-1560 A/B
Duty Propane Reflux Pump (Depropaniser)
Manufacturer BW/IP Inter.Co.
Driver Electric Motor
Motor Motor Speed 2970 rpm
Gear box None
Pump Type Horizontal Barrel Type
Suctions Single
Stages Two
Seals Pressurised Seal System
Fluid Pumped Propane
Design Temperature -46C approx.
Sealant medium Aeroshell 31/41

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P-1570 A/B
Duty Debutaniser Reflux Pumps
Manufacturer BW/IP International B.V.
Driver Electric Motor
Motor Speed 2950 RPM
Gear box None
Pump Type Horizontal Barrel type
Suctions Double
Stages 5 stage
Seals Pressurised System
Fluid Pumped Butane
Temperature -8C approx.
Sealant medium Aeroshell 31/41

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P-1580 A/B
Duty LPG Re-injection Pumps
Manufacturer Sundstrand
Driver Electric Motor
Motor Speed 9466 RPM
Gear Box Yes. 9419 rpm final gear
Pump Type Centrifugal
Suctions Single
Stages Single
Seals Pressurised System
Fluid Pumped LPG
Temperature -30C approx.
Sealant medium Aeroshell 31/41

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P-1101 A/B Amine Charge Pumps
Manufacturer BW/IP
Driver Electrical motor
Motor Power 850 kW
Motor Speed 2980 rpm
Gear Box None
Pump Type Centrifugal
Suctions Single
Stages 4
Seals Crane 8B1/AR151
Fluid Pumped Lean Amine with dissolved gases
Temperature 55ºC
It takes fluid from the pump discharge through a pipe and flushes the seal
chamber and empty itself back to the product

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P-4101
Duty HTF Circulation Pumps
Manufacturer BW/IP Internationale BV
Driver Electric Motor
Motor Speed 1450rpm
Pump Type Centrifugal
Suctions Double
Stages Single
Seals Crane 215 metal bellows, mech seal cartridge type.
Fluid Pumped HTF Shell Thermia B
Temperature 139.6oC
.

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P-4111A/B
Duty HTF Circulation Pumps
Manufacturer BW/IP Internationale BV
Driver Electric Motor
Motor Power 580kW
Motor Speed 1450rpm
Gear box None
Pump Type Centrifugal
Suctions Double
Stages Single
Seals Crane 215 metal bellows, mech seal cartridge type.
Fluid Pumped HTF Shell Thermia B
Temperature 191oC
Fluid is taken to the seal chamber from pump discharge, cool the
seal faces
and discharges it back through a discharge pipe to the product line

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Thank
you